Lithium Iron Phosphate Batteries; LFP; LiFePO4 discussions

Re: Lithium Iron Phosphate Batteries; LFP; LiFePO4 discussions

john p wrote: »

...for almost 45yrs so have trued and seen almost everything.

Ya might have me beat by ~10yrs. Makes me feel young.:D

Still, that's a prideful claim. Can't imagine what I might do or have done (much of which I am reticent to admit) that would allow me to make a similar claim. Just me. :-)

Might make a interesting reality show. :roll:

Stepping out of the flames... I am thinking of getting 60AH @ 12V worth of this battery type for a mobile (human powered) application that I have been working on for sometime. I like the lower weight and DoC capabilities.

Enjoy!

K

Re: Lithium Iron Phosphate Batteries; LFP; LiFePO4 discussions

So if one cell is out of limits, the bank is disconnected??

Or, one cell gets full charge; then are others that lag left behind?

Or, one cell gets depleted while others have sufficient capacity and the load is cut off?

I believe you guys when you say it works... I just need to better understand how it does!

K

Re: Lithium Iron Phosphate Batteries; LFP; LiFePO4 discussions

Kamala you are looking at it to closely. you seem to be thinking there are going to be big differences between cells there isnt. As I said earlier cell difference is only about .15 of a v at worst case .
as you can see if all other cells at say 2.6v the worst one be at 2.32v now lets say its a 12 batt 4 cells so 3 at 2.6v =7.8v plus one at 2.42v total 10.22 v ok but the battery management would be set to opperate a turn off supply relay or bring in a charger at 10v.
is that better to understand?

Kamala re read post #90 again im sure you missed something or mabe my explanation was not clear if so just reask and Iwill try to explain it another way.

Re: Lithium Iron Phosphate Batteries; LFP; LiFePO4 discussions

The one wire from the 600 mA shunts appears to be nothing but a normally closed relay. If the battery is outside the 2.0 to 4.3 vdc range the relay opens up. All the normally closed relays are connected in series so any single battery can open the chain. The relay isolates the one wire from battery and any stack voltage point.

As to the 600 mA shunt limit, this boils down to a reasonable power dissipation on the shunts. It could be made with a rather large heat sink that might raise the heat dissipation to 5 or 6 watts but that is still only 1.6 amps shunting. The batteries seem to be approaching full charge at about 3.45-3.5 vdc so the charge current is dropping off above about 3.4 vdc per cell.

The cells need to be reasonablely matched and fully charged before connecting them up in final installation series configuration.

On discharge, the battery drops out quickly below 3.0 vdc. Under a load with a series stack of batteries, the 2.0v level would be passed through quickly and possibly driven to reverse voltage unless something 'pulls the plug'.

Now how this plays in adapting to an existing battery powered inverter takes a bit of customization. For an XW as example, the one wire relay output may be connected to inverter shutdown remote control. I would set XW low batt shut down to 3.0v times number of cells and use an A-H gauge meter to try and avoid a one wire relay shutdown.

Re: Lithium Iron Phosphate Batteries; LFP; LiFePO4 discussions

Greener power thanks for putting that graph up it shows what happens better than I have explained it and now others may see it and understand how the 600ma cell ballencers work